Recently, attention has been focused on sheet material information detecting devices adapted to obtain information on a sheet material to discern the kind of sheet material.
In U.S. Pat. No. 6,291,829, there is proposed a sheet material information detecting device mounted in an image forming apparatus, in which light is emitted toward a recording medium from a light source arranged along a recording medium path and in which the intensity of the radiation from the surface of the recording medium is detected by a sensor, thereby discerning the kinds of recording mediums.
However, due to the demand for a reduction in the size of image forming apparatuses, the recording medium path is curved in many cases. Further, the recording medium transporting speed has been increased. Thus, the sheet material, such as a recording medium, flutters as it is transported, so that its angle with respect to the light source and the sensor is not fixed, resulting in fluctuation in the accuracy in information detection.